Hourglass dolphin description

The small and robust hourglass dolphin (Lagenorhynchus cruciger) is often nicknamed the ‘sea cow’ due to its characteristic black and white colouring. Its common name refers to the two white patches connected by a thin white strip on each flank, which bear resemblance to an hourglass. The species name cruciger is Latin for ‘cross-bearing’, referring to the black and white pattern on the back of the dolphin which resembles a cross when viewed from above (6)(7).

The hourglass dolphin is easily distinguished from the similarly sized southern right whale dolphin (Lissodelphis peronii), as unlike the southern right whale dolphin, it has a dorsal fin. The dorsal fin varies significantly between individuals, but it is generally tall and curved (6). It is thought that the curve is perhaps more pronounced in older individuals (3).

The male hourglass dolphin is thought to be slightly shorter than the female, although this observation is based on a limited number of specimens (6).

Related species

Hourglass dolphin biology

A sociable species, the hourglass dolphin is usually observed travelling in small groups of between 1 and 8 individuals, although groups of up to 60 have been seen (7).

The hourglass dolphin appears to enjoy riding bow waves and wakes, and has been observed altering its direction to catch the waves created by travelling boats and ships (10). It has also been observed riding the bow waves of whales, regularly jumping out of the water as it plays around the larger animals (11). Whalers have historically searched for this characteristic behaviour in order to locate the fin whale (Balaenoptera physalus). The hourglass dolphin has also been seen interacting with a variety of other whale species, as well as the southern right whale dolphin (Lissodelphis peronii) (12).

Little is known about the feeding habits of the hourglass dolphin, but scientists have recorded small fish, crustaceans and squid from the stomach contents of several specimens (13)(14). This species has also been observed feeding in plankton swarms and seabird aggregations (13).

Like all toothed whales, the hourglass dolphin uses echolocation for orientation and prey location. A recent study showed that this species produces very high-pitched clicks, which allow it to detect prey at more than twice the distance of other dolphin species (15). It is thought that the hourglass dolphin is likely to communicate using sight and touch (6).

Knowledge of the parental behaviour of the hourglass dolphin is limited; however, it is known that the female will nurse its young from birth, and based on data from other species in the Lagenorhynchus genus, it is thought that lactation lasts for 12 to 18 months (6).

Hourglass dolphin range

The hourglass dolphin is distributed in the Antarctic region, where it occurs around the higher latitudes of the southern oceans (1). It is the only oceanic dolphin species which is regularly found south of the Antarctic Convergence, where the colder waters of the Antarctic meet the warmer waters of the sub-Antarctic (8). The range of the hourglass dolphin is known to extend to the Antarctic ice-edges in the south, although its distribution to the north is less well known (1).

The hourglass dolphin is most commonly seen around the Antarctic Convergence, between South America and Macquarie Island, although it has also been seen off the south coast of New Zealand, near the South Shetland Islands, and around the Tierra del Fuego province (9).

It is usually found in southern waters during the summer months and northern waters during the winter, suggesting that this species migrates seasonally following the cold-water currents (9).

Hourglass dolphin status

Hourglass dolphin threats

There are currently no known specific threats to the hourglass dolphin (1). It is thought that the species is probably preyed upon by killer whales, but there hasn’t yet been any documented evidence of predation. The hourglass dolphin is not commercially hunted and accidental bycatch is limited (6).

Glossary

Bycatch

In the fishing industry, the part of the catch made up of non-target species.

Crustaceans

Diverse group of animals with jointed limbs and a hard external skeleton, characterised by the possession of two pairs of antennae, one pair of mandibles (mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps, woodlice and barnacles.

Dorsal fin

The unpaired fin found on the back of the body of fish, or the raised structure on the back of most cetaceans (whales, dolphins and porpoises).

Echolocation

Detecting objects by reflected sound. Used by bats and odontocete cetaceans (toothed whales, dolphins and porpoises) for orientation and to detect and locate prey.

Genus

A category used in taxonomy, which is below ‘family’ and above ‘species’. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial’ Latin species name; the second part is the specific name.

Plankton

Aquatic organisms, usually tiny, that drift passively with water movements; includes phytoplankton (plants), zooplankton (animals), or other organisms such as bacteria.

Goodall, R.N.P. (1997) Review of sightings of the hourglass dolphin, Lagenorhynchus cruciger, in the South American sector of the Antarctic and the sub-Antarctic. Reports of the International Whaling Commission, 47: 1001-1014.

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